Constant wattage autotransformer ballast for high pressure sodium lamp

ABSTRACT

A ballast for a high pressure sodium lamp includes a constant wattage autotransformer with a series capacitor, of 10 microfarads for example, between the autotransformer secondary and one lamp terminal, and an arc sustaining capacitor of lower value connected in parallel with the secondary.

United States Patent 1191 Paget et al.

[ Nov. 6, 1973 [22] Filed:

[ CONSTANT WATTAGE AUTOTRANSFORMER BALLAST FOR HIGH PRESSURE SODIUM LAMP [75] Inventors: Fredrick W. Paget, Rockport; John [73} Assignee: GTE Sylvania Incorporated,

Danvers, Mass.

Jan. 2, 1973 [21] Appl. No.: 320,139

[52] US. Cl 333/20, 315/239, 315/241, 315/276 [51] Int. CLHOSb 37/00, HOSb 41/16, HOSb 41/233 [58] Field of Search ..3l5/5759, 227, 232, 239, 315/241, 242, 244-245, 276, 279, 282;

[56] References Cited UNITED STATES PATENTS 3,029,363 4/1962 Mauerer 315/239 x 2,910,623 10/1959 Yaeger 315/241 I Primary Examiner--Rudolph V. Rolinec Assistant ExaminerMarvin Nussbaum Attorney-Norman J. OMalley et al. I

[57] ABSTRACT A ballast for a high pressure sodium lamp includes a constant wattage autotransformer with a series capacitor, of 10 microfarads for example, between the autotransformer secondary and one lamp terminal, and an arc sustaining capacitor of lower value connected in parallel with the secondary.

5 Claims, 5 Drawing Figures PAIENTEDnuv s 1915 I FIG..2

FIG. 4

FIG.5

TIME

, 1 CONSTANT WATTAGE AUTOTRANSFORMER BALLAST FOR HIGH PRESSURE SODIUM LAMP BACKGROUND or THIE INVENTOR High pressure mercury lamps have been in use for decades in street lighting and industrial plants To provide the necessary starting and operating voltage for such mercury lamps constant wattage autotransformer (CWA) ballasts have been installed in millions of mercury lamp fixtures throughout the world. Presently, owing to its superior efficiency and longer life the high pressure sodium (HPS) lamp is increasingly rapidly replacing th emercury lamp. HPS lamps, however, do not stabilize their are as do mercury lamps but vary their voltage with temperatures. Consequently it has hitherto been considered necessary, and it has been the practice to completely replace existing CWA ballasts with a new reactor type of ballast. l

It is the object of the present invention to provide a simple way of modifying the millions of existing mercury lamp ballasts so that they will operate I-IIS lamps, thus avoiding the expense of replacing such ballasts with new reactor ballasts.

STATEMENT OF INVENTION According to the invention a ballast for high pressure sodium lamps comprises input terminals for connection to alternating current lines, output terminals for connection across a high pressure sodium lamp, a constant wattage autotransformer having a primary winding connected to the input terminals and one output terminal, and a secondary having a connection to the other output terminal, series capacitor in the connection to the other output terminal, and an arc sustaining ca'paci tor connected to one of, the input terminals in parallel with the secondary winding of the autotransformer and having a value to resonate therewith, whereby to produce afast rise in the voltage at the output terminals at the beginning of each alternating high cycle, thereby to sustain and stabilize the arc in a high pressure sodium lamp.

DRAWINGS FIG. 5 is a graphcomparing HPS larnp voltages with prior and present CWA ballasts.

DESCRIPTION The typical I-IPS lamp installation of FIG. 1 comprises a ballast B sealed or potted in a housinglI-Il The ballast has alternating current input terminals Aand C for connection to 1 volt lines and output terminals 1 and 2 for connection to a high pressure sodium lampL such as Sylvania Lumalux 2. Usually one of the' lamp terminals, e.g., 2, is connected to'a common input terminal, e.g., C. The ballast includes an autotransformer T having a primary winding T1 and secondaryTZ on a core having" an air gap G indicated by a conventional symbol. Connected between the secondary T2 and one output terminal is a capacitor C1 usually of 10 or more microfarads value. Being connected in series with the transformer T and lamp L the capacitor C1 Iimitsor controls the lamp current and improves the power factor of the entire load, and is usually potted with the transformer T in the ballast H.

As previously explained the CWA ballast described is practically incapable of starting or maintaining discharge of the I-IPS lamp and has been replaced with a reactor type ballast with a high voltage pulsing device. According to the form of the invention shown in FIG. 1 such a ballast will start and sustain an easy start lamp by the connection of an 0.1 to about 10 microfarad capacitor C2 to the ballast output terminal 1 and input terminal C in parallel with the secondary T2. Similarly, as shown in FIG. 3, a sustaining capacitor C4 (as contrasted with the series capacitor C1) is connected be tween the output terminal 1 andinput terminal A. In both cases the terminals 1, A and C are exposed externally of the ballast housing H and the connection of the sustaining capacitor C2 or C4 may be made in an existing CWA ballast installation without removing or unhousing the ballast.

While the above sustaining capacitor connections are preferred, CWA ballasts may be assembled with the sustaining capacitor in the housing. In FIG. 2 a sustaining capacitor C3 is connected to the output end of the transformer secondary and the common input terminal C. In FIG. 4 a sustaining capacitor C5 is connected directly across the secondary T2.

In each of the four examples of FIGS. 1 to 4 the sustaining capacitor is in parallel with the autotransform er secondary T2 and reacts with the secondary creating sharper transitions in the alternating voltage applied, to the lamp at the time when the alternating current passes through zero.

FIG. 5 shows the voltage applied by CWA ballast,

5* G.E. CWA No. 9T65W27l4G1 without a sustaining capacitor, solid line X, and with a l microfarad sustaining capacitor, broken line Y. The solid line lamp voltage X obtained with the CWA ballast lacking a sustaining capacitor has a substantially lower peak value than thatof curve Y. Also the time tx between the instant voltage X crosses O and its peak is substantially longer than the corresponding time ty of voltage Y (with sustaining capacitor). In practice the lamp with voltage X did not start reliably, was not stable in operation, extinguished intermittently. In contrastthe lamp voltage Y applied from an identicalCWA ballast with a sustaining capacitor'produced ignition nearly twice as fast as with voltage X, caused the HPS lamp to stabilize its arc in continuous, reliable operation, and when the lamp was artificially extinguished caused the lamp to re-ignite in 60 percent less time than with voltage X.

The above described improved operation can be obtained with sustaining capacitors between 0.1 and approximately IO microfarads value. Below 0.1 microfarads the sustaining characteristic is weak; above 10 microfarads the expense and bulk of the sustaining capacitor outweigh any improvement in performance of the ballast.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

We claim:

l. A ballast for a high pressure sodium lamp comprismg:

input terminals for connection to alternating current lines,

output terminals for connection across a high pressure sodium lamp,

a constant wattage autotransformer having a primary winding connected to the input terminals and one output terminal, and a secondary having a connection to the other output terminal,

a series capacitor in the connection to the other output terminal, and

an arc sustaining capacitor connected to one of the input terminals in parallel with the secondary winding of the autotransformer and having a value to resonate therewith,

whereby to produce a fast rise in the voltage at the output terminals at the beginning of each alternating half cycle, thereby to sustain and stabilize the ing capacitor has a value of 0.4 to l microfarad. 

1. A ballast for a high pressure sodium lamp comprising: input terminals for connection to alternating current lines, output terminals for connection across a high pressure sodium lamp, a constant wattage autotransformer having a primary winding connected to the input terminals and one output terminal, and a secondary having a connection to the other output terminal, a series capacitor in the connection to the other output terminal, and an arc sustaining capacitor connected to one of the input terminals in parallel with the secondary winding of the autotransformer and having a value to resonate therewith, whereby to produce a fast rise in the voltage at the output terminals at the beginning of each alternating half cycle, thereby to sustain and stabilize the arc in a high pressuRe sodium lamp.
 2. A ballast according to claim 1 wherein the autotransformer and series capacitor are sealed in a housing and the sustaining capacitor is connected to the ballast terminals externally of the housing.
 3. A ballast according to claim 1 wherein the sustaining capacitor has a lower value than the series capacitor.
 4. A ballast according to claim 1 wherein the sustaining capacitor has a value between 0.1 and 10 microfarads.
 5. A ballast according to claim 4 wherein the sustaining capacitor has a value of 0.4 to 1 microfarad. 